trackingIdInput = new TextField<String>( "trackingIdInput", new PropertyModel<String>( this, "trackingId" ) );
add( trackingIdInput.setRequired( true ).setLabel( Model.of( "Cargo" ) ).setOutputMarkupId( true ) );
trackingIdSelector = new DropDownChoice<String>( "trackingIdSelector",
new PropertyModel<String>( this, "trackingIdSelected" ),
fetch.cargoIds() );
trackingIdSelector.add( new AjaxFormComponentUpdatingBehavior( "onchange" )
{
@Override
protected void onUpdate( AjaxRequestTarget target )
{